In recent years, an increase in the amount of industrial wastes discharged from plants and facilities has become a striking social problem. Among such industrial wastes, waste liquid has a great impact upon the environment, because discharge volume thereof is huge. In conjunction with mounting concerns about environmental issues, effluent standards with respect to waste liquid containing heavy metals have become more rigorous. Under such circumstances, in order to evaluate the potential hazard of waste liquid, there is demand for a simple method for determining heavy metal concentration of waste liquid with high sensitivity.
Among heavy metal species contained in waste liquid, copper is eluted from copper pipes and brass parts employed for water supply equipment or for transportation of mine wastewater, industrial wastewater, etc., and is present as a copper sulfate or copper chloride to be used as an organism inhibitor; and long-term drinking of water containing a high level of copper resulted from above factors as well as pesticide contamination is known to make the skin and hair greenish and to cause other conditions.
One typical method for determining heavy metal in waste liquid is measuring absorbance of each target element—metal indicator complex. A variety of metal indicators each having a specificity for a target element is known in the art.
Meanwhile, azo compounds having a substituent such as an amino group, a hydroxyl group, or a sulfonate group have been employed as dyes. Some azo dyes form a complex with a metal ion with change in color of the corresponding free dyes. Hitherto, a variety of metal indicators exhibiting such color change have been employed.
Examples of the azo compounds generally employed as a metal indicator for copper ions (hereinafter referred to as copper ion indicator) include 2-(5-bromo-2-pyridylazo)-5-[N-(n-propyl)-N-(3-sulfopropyl)amino]phenol disodium salt dihydrate (5Br.PAPS, product of Dojindo Laboratories), 2-[1-(2-hydroxy-5-sulfophenyl)-3-phenyl-5-formazano]benzoic acid sodium salt (Zincon, product of Dojindo Laboratories), 1-(2-pyridylazo)-2-naphthol (PAN, product of Dojindo Laboratories), a reagent (mixture of PAN and Cu-EDTA, Cu-PAN, product of Dojindo Laboratories), 2-(5-bromo-2-pyridylazo)-5-[N-(n-propyl)-N-(3-sulfopropyl)amino]aniline sodium salt (5Br.PSAA, product of Dojindo Laboratories), and 4-(2-pyridylazo)resorcinol (PAR, product of Dojindo Laboratories) (Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2000-338096